scholarly journals Mechanical Characteristics for Rocks under Different Paths and Unloading Rates under Confining Pressures

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Bing Dai ◽  
Guoyan Zhao ◽  
Longjun Dong ◽  
Chen Yang
Keyword(s):  
Mechanical Characteristics ◽  
Axial Strain ◽  
Initial Point ◽  
Strain Increment ◽  
Triaxial Tests ◽  
Lateral Strain ◽  
Dilatancy Angle ◽  
Peak Point ◽  
Confining Pressures ◽  
D Value

To investigate mechanical characteristics of rocks under different unloading conditions, triaxial tests are carried out with initial confining pressures of 10, 20, and 30 MPa and unloading rates of 0.05~1 MPa/s in three stress paths. Results show that the increment of axial strain is far less than that of the lateral strain. The unloading rates of confining pressures have less influence on variation of strain and lateral increment in path I. The variation of axial increment strain in the same time is slightly larger than the variation of lateral increment; D-value is influenced by unloading rates of confining pressures in path II. The variation of axial strain increment decreases firstly and then increases with the variation of confining pressures. The relation decreases and then increases with unloading rates increases in path III. The dilatancy angle decreases with initial confining pressures increases. The vary rates of dilatancy angle from initial point of dilatancy angle to peak point of dilatancy angle increase with the unloading rates of confining pressures. In the same rates, the vary rates of dilatancy angle from the initial point of the dilatancy angle to peak point of the dilatancy angle in path I are greater than those in path II.

scholarly journals Study on Lateral Deformation and Failure Characteristics of Coal Based on Different Confining Pressures

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Jian-jun Ren ◽  
Shan-Yang Wei ◽  
Shi-Hai Shu ◽  
Wei-Dong Luo
Keyword(s):  
Axial Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Lateral Strain ◽  
Lateral Deformation ◽  
Axis Ratio ◽  
Deformation And Failure ◽  
Initial Stage ◽  
Confining Pressures ◽  
Potential Parameters

To study the lateral deformation characteristics of coal under different confining pressures, coal compression experiments with confining pressures of 0 MPa, 3 MPa, 5 MPa, and 7 MPa were conducted under the same loading rate by using the TAW-2000 electrohydraulic servo rock mechanics experimental machine. The results of the study showed the following: at the initial stage of loading, the lateral strain of coal was about 12.22%–46.9% of the axial strain at the elastic deformation stage and 41.18%–64.96% of the axial strain at the inelastic deformation to peak stress stage. Compared with the experiment under 0 MPa confining pressure, the growth rate of the lateral strain of the coal under 3 MPa, 5 MPa, and 7 MPa confining pressures was much smaller than that of the corresponding axial strain. When the coal was damaged under different confining pressures, the lateral strain was maintained at about 0.6 × 10−2. Based on the field verification, we proposed that the lateral strain during the coal failure and the nonlinear region of the lateral axis ratio changing with time can be used as potential parameters for predicting the coal failure.

scholarly journals Experimental Study on Viscoplastic Property of Unsaturated Reticulate Red Clay Used as an Engineered Barrier

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Chuang Zhang ◽  
Jian-Zhong Li ◽  
Yong He
Keyword(s):  
Axial Strain ◽  
Confining Pressure ◽  
Matric Suction ◽  
Triaxial Tests ◽  
Red Clay ◽  
Reticulate Red Clay ◽  
Confining Pressures ◽  
Loading Tests ◽  
Engineered Barrier ◽  
The Relationship

In this study, to explore the feasibility of a compacted red clay as an engineered barrier in landfills, the viscoplastic property of remodeled unsaturated reticulate red clay was studied through a series of triaxial tests. According to the deviatoric stress–axial strain curves obtained through loading tests with varying strain rates and under different conditions, the viscoplastic parameter β of remodeled reticulate red clay was obtained. The effects of different matric suctions and net confining pressures on the viscoplasticity of unsaturated reticulate clay were analyzed. The test results showed that remodeled reticulate red clays with different degrees of saturation have similar viscoplastic properties, and their stress–strain curves are all isotach. The stiffness of unsaturated reticulate red clay increased with increasing confining pressure and matric suction. The relationship between β and the net confining pressure can be described using a linear equation. The β value of the specimens increased with increasing matric suction under a constant net confining pressure. A similar linear relationship was observed between β and the matric suction. These relationships are explained considering the loading rate effect mechanism.

scholarly journals Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

2021 ◽  
Author(s):  
Valerian Schuster ◽  
Erik Rybacki ◽  
Audrey Bonnelye ◽  
Johannes Herrmann ◽  
Anja M. Schleicher ◽  
...  
Keyword(s):  
Young’S Modulus ◽  
Deformation Behavior ◽  
Water Saturation ◽  
Young's Modulus ◽  
Axial Strain ◽  
Shear Zones ◽  
Opalinus Clay ◽  
Triaxial Tests ◽  
Influence Of Water ◽  
Confining Pressures

AbstractThe mechanical behavior of the sandy facies of Opalinus Clay (OPA) was investigated in 42 triaxial tests performed on dry samples at unconsolidated, undrained conditions at confining pressures (pc) of 50–100 MPa, temperatures (T) between 25 and 200 °C and strain rates ($$\dot{\varepsilon }$$ ε ˙ ) of 1 × 10–3–5 × 10–6 s−1. Using a Paterson-type deformation apparatus, samples oriented at 0°, 45° and 90° to bedding were deformed up to about 15% axial strain. Additionally, the influence of water content, drainage condition and pre-consolidation was investigated at fixed pc–T conditions, using dry and re-saturated samples. Deformed samples display brittle to semi-brittle deformation behavior, characterized by cataclastic flow in quartz-rich sandy layers and granular flow in phyllosilicate-rich layers. Samples loaded parallel to bedding are less compliant compared to the other loading directions. With the exception of samples deformed 45° and 90° to bedding at pc = 100 MPa, strain is localized in discrete shear zones. Compressive strength (σmax) increases with increasing pc, resulting in an internal friction coefficient of ≈ 0.31 for samples deformed at 45° and 90° to bedding, and ≈ 0.44 for samples deformed parallel to bedding. In contrast, pre-consolidation, drainage condition, T and $$\dot{\varepsilon }$$ ε ˙ do not significantly affect deformation behavior of dried samples. However, σmax and Young’s modulus (E) decrease substantially with increasing water saturation. Compared to the clay-rich shaly facies of OPA, sandy facies specimens display higher strength σmax and Young’s modulus E at similar deformation conditions. Strength and Young’s modulus of samples deformed 90° and 45° to bedding are close to the iso-stress Reuss bound, suggesting a strong influence of weak clay-rich layers on the deformation behavior.

scholarly journals Critical State Model of Sand-Tire Derived Aggregate Mixtures Based on Triaxial Tests

2021 ◽  
pp. 036119812199783
Author(s):  
Adolfo Foriero ◽  
Nima Ghafari
Keyword(s):  
Critical State ◽  
Axial Strain ◽  
Friction Angle ◽  
Critical State Model ◽  
State Model ◽  
Triaxial Tests ◽  
Experimental Program ◽  
Modified Cam Clay ◽  
Tire Derived Aggregate ◽  
Confining Pressures

This study is part of an environmental experimental program on the use of scrap automobile tires for geotechnical applications. Different types of laboratory tests were conducted to determine the elastic, plastic, and creep parameters of tire derived aggregate (TDA)-sand granulated mixtures. However, this paper emphasizes the plasticity parameters via the development of a critical state model based on the results of triaxial tests. This was attained by considering loose sand specimens, at a predetermined TDA volumetric content, subject to three different confining pressures under a constant axial displacement rate. The calculated deviatoric stress versus axial strain curves, obtained via the modified Cam Clay model, captured the non-linear elastoplastic response obtained in the tests. Results indicated that the level of the shear strength is highly dependent on critical state friction angle which in turn depends on the TDA content. For the loose TDA-sand mixtures used in the present study, the effect of the TDA content demonstrates a reinforcement of the sand matrix. However this reinforcement diminishes as the TDA content increases.

scholarly journals A Nonlinear Constitutive Model for Disintegrated Carbonaceous Mudstone Based on Logarithmic Functions

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xiang Qiu ◽  
Jinhong Li ◽  
Huangbin Jiang ◽  
Hongyuan Fu ◽  
Shun Yang
Keyword(s):  
Constitutive Model ◽  
Axial Strain ◽  
Confining Pressure ◽  
Deviatoric Stress ◽  
Triaxial Tests ◽  
Lateral Strain ◽  
Logarithmic Function ◽  
Stress Strain ◽  
Nonlinear Constitutive Model ◽  
Nonlinear Stress

To study the mechanical characteristics of the disintegrated carbonaceous mudstone (DCM), consolidated drained triaxial tests were conducted on the DCM with three degrees of compaction (i.e., 90%, 93%, and 96%). Then, the nonlinear constitutive model suitable for the DCM was established based on test results using a logarithmic function. The stress-strain characteristics of the DCM were analyzed. The results revealed that the axial strain of the DCM was positively correlated with the deviatoric stress and lateral strain. The slopes of deviatoric stress-axial strain curves decreased with the increase of axial strain and so did the slopes of the axial strain-volumetric strain curves. The strength of the DCM increased with the increase of the confining pressure and the degree of compaction. In addition, the axial strain induced by dilatancy was also positively correlated with the degree of compaction and the confining pressure. Furthermore, under triaxial loading conditions, the relationship between the stress and strain of the DCM can be expressed by a logarithmic function; based on this, a nonlinear constitutive model with ten material parameters was derived. In addition, the results of numerical tests using the model showed similar stress-strain characteristics of the DCM comparing with the triaxial tests. Hence, it indicated that the nonlinear constitutive model based on the logarithmic function can reflect the nonlinear stress-strain characteristics of the DCM.

Strength Attenuation and Post Failure Behaviour of Fine Sandstone

2012 ◽  
Vol 446-449 ◽  
pp. 3538-3543
Author(s):  
Ji Jun Zhou ◽  
Huai Fu ◽  
Yue Zhang ◽  
Yan Li ◽  
De Zhang
Keyword(s):  
Shear Test ◽  
Fractured Rock ◽  
Axial Strain ◽  
Confining Pressure ◽  
Lateral Strain ◽  
Material Strength ◽  
Failure Behaviour ◽  
Block Shear ◽  
Stress Peak ◽  
Confining Pressures

Three types of physical tests were designed to study post failure behaviour and strength attenuation of fine sandstone. Tests include rock compression test, rock unloading test and rock block shear test. The stress-strain curves at different confining pressures had been obtained as well as axial strain-lateral strain curves. The differences of axial strain-lateral strain curves exhibit that stress peak point and the point of fault formation are apparently different for the rock. After the fault is generated, fractured rock slides on the fault surfaces, while confining pressure, material strength and structure effect decide the post failure behaviour. Damaged rock specimens were poured in concrete specimens as well as irregular blocks. Material strength of rock blocks was attained. Shear strength gradually attenuates with unloading points close to the peak. Past the stress peak, rock blocks from fractured rock still have considerable material strength. It is shown that there are differences of strength parameters obtained from direct shear test and triaxial test.

scholarly journals Deformation and Acoustic Emission Characteristics of Cracked Granite during Creep

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Chunping Wang ◽  
Jingli Xie ◽  
Jian Liu
Keyword(s):  
Acoustic Emission ◽  
Axial Strain ◽  
Failure Process ◽  
Deformation Characteristic ◽  
Temporal Distribution ◽  
Confining Pressure ◽  
High Energy ◽  
Lateral Strain ◽  
Creep Tests ◽  
Confining Pressures

A series of multistage creep tests under different confining pressures with acoustic emission monitoring have been performed to investigate the deformation characteristic and failure process of cracked granite during creep. The critical axial strain of cracked sample showed an increasing tendency with the increase of confining pressure. In contrast, critical lateral strain experienced a process of descending first at low confinement and then remaining nearly constant at high confinement. Compared with loading-cracked specimen, smaller critical axial strain, greater critical lateral strain, and higher lateral creep strain rate were found for unloading-cracked specimen. Based on the spatial and temporal distribution of acoustic emission events, the cracking process during creep was analysed. The AE events with high energy are mainly concentrated at the final fracture area of the specimen. The higher the confining pressure, the more the AE events with low energy. Compared with the loading-cracked specimen, the percentage of AE events with high energy is relatively small for the unloading-cracked specimen.

scholarly journals Mechanical Characteristics and Failure Characteristics of Jointed Rock under Axial Unloading and Radial Unloading

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Tielin Han ◽  
Junping Shi ◽  
Yunsheng Chen
Keyword(s):  
Inclination Angle ◽  
Mechanical Characteristics ◽  
Axial Strain ◽  
Radial Pressure ◽  
Confining Pressure ◽  
Jointed Rock ◽  
Lateral Strain ◽  
Failure Characteristics ◽  
Deformation Properties ◽  
Cracked Specimens

In this research, we used precracked rock-like materials (simulating jointed rock masses) to assess the triaxial compression of cracked specimens under axial unloading and radial unloading paths. The research goal was to comparatively analyze and research the mechanical characteristics of cracked specimens to ascertain how deformation properties, strength properties, and failure features influence the overall mechanisms in context. The test results showed that the failure of specimens did not appear at peak stress under axial unloading and radial unloading. The elastic stage, yield stage, and failure stage of the stress-strain curves were not clearly defined in the testing process. However, the stress drop and the strain of resilience of the lateral strain-axial strain curve happened under this path because the lateral strain was significantly greater than the axial strain. This in turn led the volumetric strain to remain in a state of expansion throughout the testing process. The mechanical properties under this path are mainly influenced by the crack inclination angle, the unloading speed of radial pressure, and the initial confining pressure. However, there is a difference in the influence of these three factors on their mechanical parameters; that is, the influence of the crack inclination angle is the greatest, followed by that of the initial confining pressure, while that of the unloading speed of radial pressure is relatively small. Finally, the failure characteristics of specimens often present mixed tension-shear failure under axial unloading and radial unloading.

scholarly journals Optical Coherence Elastography Techniques for Carotid Arterial Wall Imaging

2021 ◽  
Author(s):  
Felix Nolte
Keyword(s):  
Axial Strain ◽  
Image Correlation ◽  
Arterial Blood Flow ◽  
Lateral Strain ◽  
Optical Coherence ◽  
Phantom Experiment ◽  
Arterial Blood ◽  
Speckle Patterns ◽  
Imaging Mode

In this thesis, elastography is evaluated in combination with optical coherence tomography (OCT). Two approaches to OCT based elastography, Digital image correlation (DIC) and Doppler optical coherence elastography (DOCE), are evaluated for an intravascular setup using in vivo images from a porcine carotid model. DIC tracks the displacement of speckle patterns in consecutive frames, allowing the calculation of axial and lateral strain. Rapid speckle decorrelation was observed in preprocessed structural images, affecting the tracking and limiting the feasibility of this algorithm. DOCE measures axial strain based on relative tissue velocities. Rotational movement of the imaging optical fibre was the biggest source of artefacts in this imaging mode, but could be removed with a newly developed algorithm, based on the phase change induced in a surrounding catheter. The standard deviation of phase after artefact removal, measured in a stationary phantom experiment, was ~0.2 rad, corresponding to a minimum detectable velocity of 792 μm/s at a Doppler angle of 20°. The sensitivity allowed the detection of arterial blood flow velocity and pattern and the detection of adjacent veins, but did not allow direct elastography.

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